1. Field of Invention
This invention relates generally to improvements in the manufacture of internal combustion engines of the type that include cylinder liners. More particularly, the invention relates to improvements in design of cylinder liners to provide larger coolant circulation passages between adjacent engine cylinder bores, and/or to reduce longitudinal dimensions of engines.
2. Description of the Prior Art
Cylinder liners are generally employed to extend engine bore life, and to provide compatible wear surfaces for the pistons and rings designed to move reciprocally within engine bores. Liners have traditionally been used in diesel engines. However, with the advent of aluminum block automotive gasoline engines, liners have recently also become commonly used in non-diesel applications.
In addition to accommodating the sealing of an engine head to an engine block, and the prevention of combustion gases from leaking into non-combustion parts of the engine, such liners must be designed to handle side loads imposed by reciprocally movable pistons, which tend to impart a slapping side-to-side motion to the liner walls. Such motion is oriented along a so-called thrust axis of the cylinder liner, and translates into side loads or forces that must be fully accommodated by the liner walls.
The typical piston is connected via a piston pin to a connecting rod. The connecting rod is connected to a crankshaft, as will be appreciated by those skilled in the art. Normally, the piston pin axis is in a plane oriented orthogonally, or at right angles, to the thrust axis plane of the piston. As such, the portion of the cylinder liner oriented along the piston pin bore axis is subject to loads less severe than those that occur along the thrust axis.
Consequently, the traditional wall thicknesses of the liners, normally designed uniformly about the circumference of the liner to accommodate the highest anticipated load, plus traditional safety factors, may be reduced along the piston pin axis portion of the liner to the extent that less of the piston thrust loads are transmitted to the liner walls in the piston pin axis region. Reduction of liner wall thickness in these areas which lie immediately between adjacent cylinder bores, would enable enhanced spacing for coolant flows between respective bores, and/or would accommodate engine designs permitting closer bores, hence smaller engine dimensions along the piston pin plane of the engine.
The present invention is an improved cylinder liner having a reduced wall thickness in a region of the liner inclusive of the piston pin plane. A traditional wall thickness of the liner is maintained in the piston thrust plane regions for appropriate resistance to high mechanical forces imposed on the liner by the ordinary side-to-side motions of a piston moving reciprocally within the liner. Such forces imparted on the liner walls by the piston tend to produce linear deflections of the liner bore, as well as of the head gasket that bears against the liner.
The reduced wall thickness of the liner affects only its external dimensions in a region along a plane passing through the piston pin axis of the liner. Thus, the bore of the liner remains fully cylindrical while the exterior of the liner is slightly elliptical. The liner has a major axis in alignment with the piston thrust plane, and a minor axis in alignment with the piston pin plane. The reduced dimension along a plane passing through the minor axis permit reduction in engine length due to shortened bore spacing requirements along the piston pin plane, and or can provide additional room for coolant to flow between adjacent cylinder liners.
Finally, such thickness reductions, applied to selective peripheral regions of the cylinder liner where such thickness is unnecessary, include additional benefits of reduced weight. Indeed, the weight benefits apply not only to the cylinder liner, but also to engines that incorporate the improved liner due to commensurately reduced engine lengths.